Nowadays, there are many fraud attempts that involve the impersonation of a person's identity. Biometrics uses the unique biological characteristics of the individual in identifying same (they are unique and non-repeatable), such as the fingerprint, the vein pattern on the palm of the hand or the rhythm of the heartbeat. Fields like Microelectronics, Photonics or Information Technology produce numerous biometric systems each year, with the intention of supplanting them as access systems.
The more biometric systems that arise, the more attempts there are at forging the biometric characteristics in question in order to “trick” the biometric sensor. Therefore, by means of artificial, lifeless materials, the hacker attempts to supplant the identity of the user that in theory will be identified as a user already registered in the access system. These attempts at fooling the biometric system are the reason behind the fear and mistrust displayed by institutions that need top security, such as banks, restricted access platforms or biometric payment gateways, as well as all electronic or information technology systems that require a biometric code to function, etc. Therefore, there are also many attempts at creating life detection systems that distinguish between the living person with their unique biometric characteristics and any replacement artificial material.
U.S. Pat. No. 6,813,010 B2 describes a biometric vein sensor known as PALM VEIN SECURE, by Fujitsu, which is used as a personal identification system. This system uses the blood capillary pattern on the palm of the hand as the unique biometric receiver element. A set of LEDs with an emission spectrum in the near-IR illuminates the palm of the hand and a CCD camera captures the image that corresponds to the radiation reflected on it. This image presents dark straight and curved sections that represent the map of blood capillaries in the hand and are due to the areas that absorb the near-IR radiation emitted by the LEDs that has not been reflected on the palm of the user's hand. The absorption of the near-IR radiation by the veins in the hand is due to the deoxidised blood haemoglobin in the blood, which presents an absorption peak of 760 nm on the electromagnetic spectrum.
As we have said before, the biometric element in Fujitsu's vein sensor, PALM VEIN SECURE, is the map of blood capillaries on the palm of the hand. At first sight, it is a biometric element that is very hard to copy because it is hidden within the tissues of the hand, but that is only at first sight, because it has already been “fooled”.
U.S. Pat. No. 6,813,010 describes a biometric sensor manufactured by HITACHI. This sensor captures as the unique biometric element the veins on a single finger of the hand of the user in question. Thus, the sensor detects the near-infrared radiation that is transmitted through the finger and emitted by LEDs whose emission band is in the near-IR and optimises the intensity of the light that arrives at the finger, so that a sharper vein pattern is obtained, making subsequent recognition easier. However, this characteristic vein pattern is simpler than the one that is gathered by FUJITSU's vein sensor for the palm of the hand, because the capture area is smaller and the mesh of capillaries is less ramified. Therefore, it is easier to copy, using the same forging procedure as is used with the FUJITSU sensor.
We have provided a brief description of two of the biometric sensors on the market that present the unique biometric element that is most difficult to forge (vein pattern). There are many others that appear in the literature and allow to identify people, such as the fingerprint sensors and those that operate according to facial recognition or hand geometry recognition, etc. Their biometric elements are unique (or almost unique), but they have the disadvantage that they are easy to replicate (using photographs, silicon fingerprints, silicon hands, etc.).
To date, only a few life detection systems for biometric sensors have been described in the literature. The majority are low-cost and are not implemented in biometric sensors because they can be easily “fooled” using simple substitution techniques. Hence, for example, when the human pulse is detected optically, it may be easily achieved by using a sheet of paper in a characteristic colour that absorbs part of the light beam that reaches the detector. Another example is the measurement of the bioimpedance of human tissue with an impedance measuring device. This measurement may be obtained using a material with an impedance that is characteristic of the characteristic biological element in question.
On the other hand, other much more advanced life detection systems that measure skin roughness, the electrical and optical characteristics of its internal layers, etc. are very expensive (they use spectrophotometers, mobile optical systems, optic fibres and waveguides, magnifying macro-lenses, CCD linear matrixes, etc.) and therefore they are not used in the biometric sensors that are available on the market.
The highlights among these developments are the following patent documents: WO 2007/027579, WO 2005/059805 and US 2005/0265586 (by the company LUMIDGIN) which employ various light sources (polarized or otherwise) in the infrared and near-ultraviolet spectrum (between 300 and 1100 nm) to observe light reflectance through skin and underlying tissue and identify certain physiological parameters that are characteristic of the individual.
European Patent EP 150330 is based on the roughness model of the tissue in the internal layer of the skin covered by the epidermal tissue, using near-infrared radiation and the analysis of different optical properties.
International patent no. WO 02/084605 also presents a device that employs light sources in the near infrared and near-ultraviolet zones of the electromagnetic spectrum to measure the absorption and reflection of light energy under the epidermis. Other related documents are as follows: WO 89/01758, EP 1834581 and US 2007/0253607. As mentioned before, these are systems that use optical elements of medium or high cost.